Common Tern in NE and offshore. Widespread on migration. Colonial. Nests on sandy or rocky beaches or islands. Hovers and dives for fish, often in concentrated flocks. Variable. ID: Compact and well proportioned. Rounded undercarriage (flat in FOTE). Narrow-based wings strongly angled back. Very light, buoyant flight. Fairly dark, often with extensive dark outer primaries. Ad br: blood-red bill with black tip. Neat black cap bordered by white reinforced by contrast with gray breast/belly. Extensive wedge to outer primaries gets darker through summer. Molts inner primaries in late summer. Upperparts darker than FOTE and ROTE. Nonbr: as adult with white on forecrown, large carpal bar (can appear small), dark bill, duller legs and darker secondary bar. 1st-s: similar and stands out among br and fresh juvs. Older worn median coverts can create a white bar. 2nd-s: typically as br but with white flecking in forecrown, dull bill and hint of carpal bar. Beware!: sick and failed breeders may look similar. Juv: upperparts dark with subterminal marks, and initially warm brown. The brown fades or feathers molted so fall birds are much grayer. Bill darkish with orangey bases becoming all dark through fall. Different head pattern from FOTE.